1. Field of the Invention
This invention relates to apparatus for tempering flat or curved glass sheets and, more specifically, apparatus that imparts a more uniform temper to glass sheets of various configurations. The sheet is heated above its annealing range and its surfaces are chilled rapidly to below the strain point while the interior is still hot. Rapid chilling continues until the entire glass sheet cools to below its strain point. This rapid cooling causes the glass sheet to develop a thin skin of compression stress surrounding an interior stressed in tension. Such a stress distribution makes the glass sheet much stronger than untempered glass so that tempered glass is likely to shatter than untempered glass when struck by an object. Furthermore, in the less frequent times when an outside force is sufficiently large to cause tempered glass to fracture, tempered glass breaks up into a large number of smoothly surfaced, relatively small particles which are far less dangerous than the larger pieces with jagged edges that result from the fracture of untempered glass.
Typical prior art tempering apparatus include nozzles extending from plenum chambers to direct a plurality of air blasts against the opposite major surfaces of a glass sheet. The prior art provides means to impart movement to the nozzles in unison relative to the glass surface to avoid directing the air blasts against fixed locations on the glass to cool the latter rapidly while other locations adjacent the fixed locations are not cooled as rapidly. Without such relative movement, patterns of iridescence form on the surface of the tempered glass. These patterns of iridescence are very annoying when viewed in reflection.
The glass tempering art has developed many techniques for imparting relative motion between the array of nozzles and the glass to avoid iridescent patterns. Some of these involve linear reciprocation of the nozzles. Others involve linear movement of glass sheets past an array of fixed nozzles. Others involve applying orbital movement (elliptical or circular) of nozzles relative to a glass sheet supported at a fixed position.
The shape of the glass sheet to be tempered and its manner of support between plenum chambers determines the best technique for providing relative movement between the nozzle arrays extending from the plenum chambers and the glass sheet to be tempered. For example, when vertically supported glass sheets are oriented with a sharp blend extending in a given direction, it is best to reciprocate the nozzle arrays in spaced vertical planes along axes parallel or approximately parallel to the given direction. When a flat glass sheet or a gently curved sheet of shallow curvature is tempered, it is usually most convenient to impart air from nozzles to which are imparted circular orbital movements that overlap corresponding movement of adjacent nozzles in spaced planes parallel to the position occupied by the glass sheet.
2. Description of the Prior Art
U.S. Pat. No. 3,849,100 to Antonio Luppino and U.S. Pat. No. 3,873,294 to Dennis M. Goolsbay disclose glass sheet tempering apparatus comprising opposing arrays of nozzles extending from spaced, opposing plenum chambers into a space therebetween containing a position that is occupied by a heated glass sheet when fluid under pressure is applied to said plenum chambers for discharge against the opposite surfaces of a glass sheet when the latter occupies said position. Means is provided with each of these apparatus to move the opposed plenum chambers in unison in either a linear reciprocating motion more suitable for sharply curved glass sheets or a closed orbital motion more suitable for flat or gently curved glass sheets. In each of these patents, each tempering nozzle of each tempering nozzle array is rigidly attached to an apertured wall of each plenum chamber and a flexible extension is applied to the inner end of each nozzle. Extensions of identical lengths are applied to provide a space to receive flat glass and extensions of different lengths are applied in a pattern to provide a curved space to receive curved glass.
Apparatus having nozzles attached to apertured plates of plenum chambers of the types disclosed in the patents to Luppino and Goolsbay were characterized by cylindrically shaped nozzles having their inner end portions externally threaded to receive inner and outer clamping nuts and washers that secured the nozzles to the apertured walls. The presence of the clamping nuts near the entrance to the apertures interrupted the smooth flow of fluid into the nozzles and thus caused a need to supply the fluid to the plenum chambers at a relatively high fluid pressure in order to deliver the fluid through the nozzles to the glass major surfaces at a rate sufficient to cool the glass major surfaces sufficiently rapidly to impart a desired degree of temper.
The energy crisis enhanced a need to develop glass tempering apparatus that delivered cold fluid to the glass surfaces at a sufficient rate of flow using as little energy as possible.
Fluid delivery systems of the prior art that improved the rate of cold fluid flow per unit of energy expended in blowing the fluid into the cold fluid supply nozzles or other delivery means required relatively thick walls for the apertures through which the cold fluid was supplied. This necessitated relatively expensive apertured walls for tempering apparatus and/or more power required to move the plenum chambers in unison in either reciprocating paths or closed orbital paths.
U.S. Pat. Nos. 2,968,126 and 3,227,540 to Richardson disclose cold fluid delivery systems comprising a series of fluid supply pipes having thick walls apertured to provide elongated passages having three different degrees of taper from their inner ends to their outer ends (U.S. Pat. No. 2,968,126) and a special shape to their inner ends including a reentrant ridge that extends toward the center of its associated supply pipe (U.S. Pat. No. 3,277,540) It is difficult and expensive to fabricate thick wall pipes to the shapes required in these patents.
U.S. Pat. No. 2,080,083 to Magnien discloses a glass tempering apparatus comprising opposed plenum chambers having outer apertured walls whose apertures for delivering cold air jets are countersunk to provide generally conically shaped inner portions merging into cylindrically shaped outer portions. No nozzles extend from the walls of the Magnien apparatus.
U.S. Pat. No. 2,118,183 to Fowler discloses nipples extending from plenum chambers through which jets of air are directed against a glass sheet. The nipple arrangement is similar to the nozzle arrangements in U.S. Pat. No. 3,849,100 to Luppino and U.S. Pat. No. 3,873,294 to Goolsbay described previously.
U.S. Pat. No. 3,881,906 to Ritter discloses apparatus for tempering glass where the plenum chambers have relatively thick walls drilled with holes and counterbored to provide conically shaped inner ends.
Other patents reported in a novelty search report as being pertinent to the present invention include U.S. Pat. Nos. 3,353,946 to McMaster, 3,455,670 to McMaster and 3,455,670 to McMaster and British Pat. No. 441,017 to Pilkington.